JPH05118751A - Method and apparatus for manufacturing super high purity nitrogen - Google Patents

Abstract

PURPOSE:To provide high purity of product nitrogen gas by a method wherein a part of liquid nitrogen after refining and separating substances of low boiling point is fed out of a refining plate lower by several stages than a refining plate at the top part of a complex refining tower while remaining oxygen is low in its volume and gas having substances of low boiling point separated through gas-liquid separation is discharged and removed. CONSTITUTION:Raw material air (B) cooled down to near its liquifying point after passing through an air filter, an air compressor, a cooling decarbonization drying device and a heat exchanger is fed into the bottom part of a medium refining tower 5 acting as a lower refining tower of a complex refining tower and refined there. Then, the refined and separated gaseous nitrogen is condensed and liquified at a condenser 15 arranged at the bottom part of a low pressure refining tower 6 acting as an upper refining tower, the condensed liquified nitrogen is fed again into the top part of the medium pressure refining tower 5 as a circulating flow. Then, a part of the circulation flow is fed out of the refining plate lower by several stages than the refining plate at the top part of the medium pressure refining tower 5, over-cooled at an over-cooler 9 and after its free expansion, the part of the super high purity liquid nitrogen gas-liquid separated through the gas-liquid separator 10 is gasified through gasification means 11 and 4 and then fed out as product nitrogen gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing ultra-high-purity nitrogen used in semiconductor manufacturing processes and containing a low boiling point component such as hydrogen, helium, or neon. The gaseous nitrogen rectified and separated from the feed air in the lower rectification column of the double rectification column is condensed and liquefied by a condenser, and the liquid nitrogen condensed and liquefied by the condenser is used as a reflux liquid at the top of the lower rectification column. The present invention relates to an ultrahigh-purity nitrogen production method and an apparatus for producing a product nitrogen gas by introducing and refluxing a part of the reflux liquid from the lower rectification column to vaporize the product.

[0002]

2. Description of the Related Art Conventionally, as a method and apparatus for producing high-purity nitrogen, gaseous nitrogen that has been rectified and separated from raw material air is condensed in a condenser, and at this time, a large amount of low-boiling components not condensed and liquefied are contained. After discharging the condensed gas to remove the low-boiling point component contained in the gaseous nitrogen from the rectification column, the condensed liquefied liquid nitrogen with a small amount of the low-boiling point component was introduced as a reflux liquid at the top of the rectification column. , A part of the liquid nitrogen introduced as a reflux liquid is discharged from a rectification plate several stages below the rectification plate at the top of the rectification column to rectify the low boiling point components contained in the liquid nitrogen. A technique for separating and producing high-purity product nitrogen has been proposed (see, for example, Japanese Utility Model Laid-Open No. 64-45290).

[0003]

The above prior art is to discharge uncondensed gas that has not been condensed and liquefied in the condenser, and to purify a part of the liquid nitrogen introduced as the reflux liquid at the top of the rectification column. The low boiling point component is removed by deriving it from the rectification plate several steps below the distillation plate to produce high-purity product nitrogen, but the low boiling point component is rectified and separated in the rectification column. At this time, as a part of the liquid nitrogen introduced as the reflux liquid is discharged from the rectification plate below the rectification plate at the top of the rectification column, product nitrogen with less low-boiling point components can be obtained, while it has high boiling point components. There is a drawback that some oxygen is likely to remain in the product nitrogen as an impurity, and there is a limit to the extent to further purify the product nitrogen. The present invention has been made in view of the above circumstances, by devising a treatment process of liquid nitrogen derived from the rectification plate several stages below the rectification plate at the top of the rectification column, the product nitrogen gas The purpose is to enable further purification.

[0004]

The first characteristic constitution of the present invention for achieving the above object is to provide a condenser for the gaseous nitrogen rectified and separated from the feed air in the lower rectification column of the double rectification column. Liquid nitrogen condensed and liquefied in the condenser is introduced as a reflux liquid to the top of the lower rectification column, and a part of the reflux liquid is discharged from the lower rectification column to produce product nitrogen gas. A method for producing ultra-high purity nitrogen, comprising: A. A step of discharging an uncondensed gas that has not been condensed and liquefied in the condenser to remove a low boiling point component contained in the gaseous nitrogen; B. A part of the liquid nitrogen introduced as the reflux liquid is discharged from a rectification plate several stages below the rectification plate at the top of the lower rectification column to refine low-boiling components contained in the liquid nitrogen. Step of separating by distillation C. A step D of supercooling the liquid nitrogen derived from the rectification plate at the lower part of the stage, performing free-expansion and gas-liquid separation, and discharging the separated gas to remove low boiling point components contained in the liquid nitrogen; ． Step of Evaporating Liquid Nitrogen Separated by the Gas-Liquid Separation The step A to D is included. A second characteristic configuration of the present invention for achieving the above object is to condense and liquefy gaseous nitrogen, which has been rectified and separated from raw material air in a lower rectification column of a double rectification column, by a condenser and condense it by the condenser. An ultra-high purity nitrogen production apparatus for producing liquefied liquid nitrogen as a reflux liquid at the top of the lower rectification column and producing a product nitrogen gas by drawing a part of the reflux liquid from the lower rectification column, , E. A discharge path for discharging uncondensed gas that has not been condensed and liquefied in the condenser; A discharge path for discharging a part of the liquid nitrogen introduced as the reflux liquid from a rectification plate several stages below the rectification plate at the top of the lower rectification column; A gas-liquid separator that supercools the liquid nitrogen derived from the rectifying plate at the lower part of the stages and performs free-expansion and then gas-liquid separation; An exhaust path for exhausting the gas separated by the gas-liquid separator, and I. And a vaporizing means for vaporizing the liquid nitrogen separated by the gas-liquid separator.

[0005]

With the structure of A, the uncondensed gas containing a large amount of the low-boiling components that have not been condensed and liquefied in the condenser is discharged to remove the low-boiling components contained in the gaseous nitrogen from the lower rectification column. After that, the condensed and liquefied liquid nitrogen having a low amount of low boiling point components is introduced as a reflux liquid to the top of the lower rectification column, and part of the liquid nitrogen introduced as the reflux liquid is partly converted into the lower rectification column by the constitution of B. The low-boiling-point components contained in the liquid nitrogen derived from the rectification plate several steps below the top rectification plate are rectified and separated, and due to the constitution of C, the low-boiling-point components that are easily vaporized are increased. By discharging the separated gas containing it, low-boiling components that could not be rectified and separated by the rectification plate are further removed, and liquid nitrogen of higher purity than the conventional one is produced. Liquid nitrogen is gasified. Further, also by the constitutions of E to I, the low-boiling component contained in the gaseous nitrogen from the lower rectification column is discharged by discharging the uncondensed gas containing a large amount of the low-boiling component not condensed and liquefied in the condenser. After removing
The condensed and liquefied liquid nitrogen with less low-boiling point components is introduced as a reflux liquid to the top of the lower rectification column, and a part of the liquid nitrogen introduced as the reflux liquid is introduced in several stages than the rectification plate at the top of the lower rectification column. The low-boiling components contained in the liquid nitrogen derived from the lower rectification plate are rectified and separated.Furthermore, by gas-liquid separation, the separated gas containing many low-boiling components that are easily vaporized is discharged and purified. The low boiling point components that could not be rectified and separated by the distillation plate are further removed to produce liquid nitrogen of higher purity than in the past, and the liquid nitrogen of high purity is gasified.

[0006]

EFFECTS OF THE INVENTION A portion of liquid nitrogen after rectifying and separating low-boiling components is rectified several stages below the rectification plate at the top of the lower rectification column with a small amount of residual high-boiling oxygen. The low-boiling point components that have been discharged from the plate and could not be rectified and separated can be removed by discharging the gas separated by gas-liquid separation, and the product nitrogen gas can be further purified.

[0007]

1 and 2 are flow diagrams showing an embodiment of an ultrahigh-purity nitrogen production method and apparatus according to the present invention, in which raw air is a medium-pressure rectification column which is a lower rectification column of a double rectification column. The condenser 15 provided at the bottom of the low pressure rectification column 6 which is the upper rectification column of the double rectification column
Is condensed and liquefied in, and the condensed and liquefied liquid nitrogen is again introduced into the top of the medium-pressure rectification column 5 as a reflux liquid, and a part of this reflux liquid is several stages higher than the rectification plate at the top of the medium-pressure rectification column 5. Derived from the lower rectification plate, further supercooled by a supercooler 9 and free-expanded, and then gas-liquid separated by a gas-liquid separator 10 to separate ultra-high-purity liquid nitrogen,
Part of this ultra-high-purity liquid nitrogen is vaporized by the heat exchangers 11 and 4 as vaporization means and is discharged as product nitrogen gas.

The raw material air passes through the air filter 1 to remove dust in the air, is guided to the air compressor 2 by the pipe P1, is compressed to a pressure of about 5 kg / cm ² G, and is guided to the pipe P2. After cooling, the cooling and decarburizing / drying unit 3 cools and removes carbon dioxide gas and water, and introduces it into the heat exchanger 4 through the pipe P3. The raw material air introduced into the heat exchanger 4 is piped from the top of the low pressure rectification column 6.
High-purity nitrogen gas introduced into the heat exchanger 4 through P19, the supercooler 9, and the pipe P20, and a waste gas pipe P12 that introduces the waste gas from the low-pressure rectification column 6 into the supercooler 7 are gas-liquid. Separator 10
Waste gas from the low pressure rectification column 6 and the gas-liquid separator 10 which are introduced into the heat exchanger 4 through the pipe P33 from the subcooler 7 by connecting the waste gas pipes P31 and P32 for discharging the waste gas from the Gas, oxygen gas introduced from the low-pressure rectification column 6 into the heat exchanger 4 through the pipe P21, ultra-high-purity nitrogen gas described later introduced into the heat exchanger 4 through the pipe P42, and medium pressure The medium-pressure high-purity nitrogen gas derived from the top of the rectification column 5 through the pipe P22 is diverted and heat-exchanged with the medium-pressure high-purity nitrogen gas introduced into the heat exchanger 4 through the pipe P44 to near the liquefaction point. Cooled and piping P4
Is introduced into the bottom of the medium pressure rectification column 5 and is rectified in the rectification sections A, B and C in the medium pressure rectification column 5 to produce nitrogen gas and liquid nitrogen at the top and an oxygen rich liquid at the bottom. To do.

The oxygen-rich liquid accumulated at the bottom of the medium-pressure rectification column 5 is piped to the liquid-air filters 8a and 8b used for switching.
After removing the hydrocarbon content introduced in P5 and concentrated in the oxygen-rich liquid, it is introduced into the supercooler 7 through the pipe P6 and the waste gas and heat from the low pressure rectification column 6 and the gas-liquid separator 10 are removed. It is exchanged and supercooled, is freely expanded by an expansion valve V1 provided in a pipe P7, is cooled, and is introduced into the upper and lower central portions of the low pressure rectification column 6 through a pipe P8. Liquid nitrogen formed in the upper and lower central portions of the medium pressure rectification column 5 is introduced from the liquid reservoir R3 into the subcooler 7 through the pipe P9 and exchanges heat with the waste gas from the low pressure rectification column 6 and the gas-liquid separator 10. It is supercooled, guided to the expansion valve V2 through the pipe P10, freely expanded and further cooled, and introduced into the upper part of the low pressure rectification column 6 through the pipe P11.

Low boiling point components (helium (H
e), hydrogen (H ₂ ), neon (Ne)) are generally about 5,000 volume PPB (VPPB) for helium and about 500 volume PPB for hydrogen.
(VPPB) and neon are about 15,000 volume PPB (VPPB), but in the oxygen-rich liquid accumulated at the bottom of the medium-pressure rectification column 5, helium is about 20 VPPB, hydrogen is about 10 VPPB, and neon is about 400 VP.
PB is dissolved, and the rest is concentrated in nitrogen gas at the top of the medium pressure rectification column 5. Then, the nitrogen gas produced at the top of the medium pressure rectification column 5 is introduced into the condenser 15 provided at the bottom of the low pressure rectification column 6 through the pipe P35 in the rectification column, and the liquid of the low pressure rectification column 6 is discharged. It is condensed and liquefied by heat exchange with oxygen. At this time, most of the low boiling point components introduced into the condenser 15 together with the nitrogen gas are not liquefied and are in a gaseous state from the lower part of the condenser 15 through the pipe P58 as an exhaust passage, and the total amount is about 1,000,000 VPPB to 20,000,000. VP
Exhausted through valve V8 as uncondensed nitrogen gas containing low boiling components of PB (about 0.1-2.0% by volume).

The liquid nitrogen condensed and liquefied in the condenser 15 is introduced as a reflux liquid into the liquid reservoir R1 of the medium-pressure rectification column 5 through a pipe P36, and the total amount of the liquid nitrogen is approximately 200,000 VPPB.
Since it contains the low-boiling point component of the above, in order to further reduce this low-boiling point component, it is rectified in the rectification section C consisting of several rectification plates provided at the top of the medium pressure rectification column 5, and the total The liquid nitrogen containing a low boiling point component of about 350 VPPB is stored in a liquid reservoir R2 provided below the rectification section C. Piping P13 as outlet from liquid reservoir R2
The liquid nitrogen derived in 1. is supercooled in the supercooler 9 by exchanging heat with the high-purity nitrogen gas (low-boiling point components total about 1,000 VPPB) derived from the top of the low-pressure rectification column 6 through the pipe P19,
Liquid nitrogen in a gas-liquid mixed state, partially vaporized, is introduced into the gas-liquid separator 10 by taking it out through the pipe P14 and freely expanding it with the expansion valve V4 to further lower the temperature. The liquid-nitrogen in the gas-liquid mixed state introduced into the gas-liquid separator 10 is gas-liquid separated, and the separated nitrogen gas contains a low boiling point component of about 3,000 VPPB in total. Introduce valve
Adjust the pressure with V5 and discharge from pipe P32. As a result,
The liquid nitrogen separated by the gas-liquid separator 10 is about 10VPPB in total.
The low boiling point component (when the low boiling point components are helium and hydrogen, the total amount is about 0.3VPPB) is purified to an ultra-high purity.

A liquid level controller LIC of the gas-liquid separator 10 so that the amount of liquid nitrogen separated by the gas-liquid separator 10 becomes substantially constant.
The ultrahigh-purity liquid nitrogen that has been separated by linking the expansion valve V4 with the expansion valve V4 is partially discharged to the heat exchanger 11 through the pipes P16 and P41 whose flow rate is controlled by the valve V6 with a flow rate controller. Pressure rectification tower 5
The medium-pressure high-purity nitrogen gas derived from the top through pipe P22 is cooled and liquefied, and is further introduced into the heat exchanger 4 through pipe P42 and vaporized by heat exchange with the raw air, resulting in ultra-high-purity product nitrogen gas. It is stored in a storage tank (not shown) through pipe P43.
The high-purity liquid nitrogen liquefied by the heat exchanger 11 is
It is introduced as a reflux liquid at the top of the medium pressure rectification column 5 through a pipe P45. Further, the remainder of the ultra-high purity liquid nitrogen separated by the gas-liquid separator 10 is a pipe P1 whose flow rate is controlled by a valve V7 with a flow rate controller.
Gas that is introduced to the top of the low-pressure rectification column 6 with a constant flow rate controlled by 7, P18 and rises in the low-pressure rectification column 6 as the reflux liquid of the rectification sections D, E, F, G of the low-pressure rectification column 6. Rectify.

The high-purity nitrogen gas introduced from the top of the low-pressure rectification column 6 to the subcooler 9 through the pipe P19 becomes high-purity nitrogen gas at room temperature and low pressure through the pipe P20 and the heat exchanger 4, and the high-purity nitrogen gas through the pipe P52. It is taken as pure product nitrogen gas. Low pressure rectification column 6
Heat is transferred from the medium-pressure rectification column 5 at its bottom to rectify at the rectification sections D, E, F, G, and produces high-purity nitrogen gas at the top and liquid oxygen at the bottom. The medium-pressure high-purity nitrogen gas introduced into the heat exchanger 4 through the pipe P44 is adiabatically expanded by the expander 13 and cooled, and introduced into the lower portion of the rectification section F of the low-pressure rectification column 6 through the pipe P46. The oxygen gas produced in the lower part of the low pressure rectification column 6 is taken out through the pipe P21, the heat exchanger 4 and the pipe P55.

Waste gas from the low-pressure rectification column 6 and the gas-liquid separator 10 introduced from the subcooler 7 to the heat exchanger 4 through the pipe P33 is discharged from the pipe P56, and a part of the waste gas is discharged. It is supplied to the cooling and slow coal drying unit 3 through the pipe P34, used for its regeneration, and then discharged through the pipe P57.

[Other Example] In the example, the nitrogen gas from the pipe P35 was cooled by the nitrogen condenser 15 and then introduced into a separately provided gas-liquid separator to condense and liquefy liquid nitrogen, which was not condensed and liquefied. It is also possible to separate the condensed nitrogen gas into gas and liquid, introduce the liquid nitrogen into the liquid reservoir R1 of the medium-pressure rectification column 5 through the pipe P36, and discharge the uncondensed nitrogen gas through the pipe P58.

It should be noted that reference numerals are added to the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a flow diagram showing a method and an apparatus for producing ultra-high purity nitrogen.

FIG. 2 is a flow diagram showing an ultrahigh-purity nitrogen production method and apparatus.

[Explanation of symbols]

 4 vaporization means 5 lower rectification column 10 gas-liquid separator 11 vaporization means 15 condenser P13 outlet path P31 discharge path P58 discharge path

Claims (2)

[Claims] 1. Gaseous nitrogen which has been rectified and separated from raw material air in a lower rectification column (5) of a double rectification column is condensed and liquefied in a condenser (15) and condensed and liquefied in the condenser (15). High-purity nitrogen for producing product nitrogen gas by introducing liquid nitrogen as a reflux liquid into the top of the lower rectification column (5) and discharging a part of the reflux liquid from the lower rectification column (5) to vaporize the product nitrogen gas. A manufacturing method, a step of discharging an uncondensed gas that has not been condensed and liquefied in the condenser (15) to remove a low boiling point component contained in the gaseous nitrogen, and a step of being introduced as the reflux liquid. A step of deriving a part of the liquid nitrogen from a rectification plate several stages below the rectification plate at the top of the lower rectification column (5) to rectify and separate low-boiling components contained in the liquid nitrogen. And the liquid nitrogen derived from the rectification plate below the above several stages was supercooled and free-expanded to be gas-liquid separated. A method for producing ultra-high purity nitrogen, which comprises a step of discharging a body to remove low-boiling components contained in the liquid nitrogen, and a step of vaporizing the liquid nitrogen separated by the gas-liquid separation. 2. The gaseous nitrogen rectified and separated from the raw material air in the lower rectification column (5) of the double rectification column is condensed and liquefied in the condenser (15) and condensed and liquefied in the condenser (15). High-purity nitrogen for producing product nitrogen gas by introducing liquid nitrogen as a reflux liquid into the top of the lower rectification column (5) and discharging a part of the reflux liquid from the lower rectification column (5) to vaporize the product nitrogen gas. In the manufacturing apparatus, a discharge passage (P58) for discharging uncondensed gas that has not been condensed and liquefied in the condenser (15) and a part of the liquid nitrogen introduced as the reflux liquid are used in the lower rectification column ( 5) Derivation path leading from the rectification plate several steps below the top rectification plate (P1
3), and a gas-liquid separator (10) for supercooling the liquid nitrogen derived from the rectification plate at the lower stage and free-expanding to separate gas and liquid.
A discharge path (P31) for discharging the gas separated by the gas-liquid separator (10), and vaporizing means (11), (4) for vaporizing the liquid nitrogen separated by the gas-liquid separator (10). Ultra-high purity nitrogen production equipment equipped with.